1. Field of the Invention
The present invention relates to a method and apparatus for manufacturing a semiconductor device, and more particularly, it relates to such, a method and apparatus for manufacturing thin films of a uniform thickness on a substrate.
2. Description of the Related Art
When thin films are formed on a substrate, a film-forming apparatus of the sheet-feed type is used as one example.
An explanation will be made of the case in which a tantalum oxide thin film (Ta2O5 film) is formed on a substrate as a concrete example. Generally, the tantalum oxide thin film is formed by means of a CVD method.
FIG. 11 is a schematic view showing one example of such conventional semiconductor manufacturing apparatuses for forming thin films of tantalum oxide on a substrate. As a raw material for the tantalum oxide thin film, pentaethoxy tantalum in a liquid state is used, and it is accommodated in a tank 21 which is disposed in a thermostatic chamber 22. The temperature of the tank 21 is controlled at a constant temperature such as, for example, 35xc2x0 C. by means of the thermostatic chamber 22. An N2 gas supplied to the tank 21 from an N2 supply piping 28 pressurizes the interior of the tank 21, so that the pentaethoxy tantalum, which is contained therein as a liquid raw material, is pushed out to a raw material supply piping 29. The pentaethoxy tantalum in the form of a liquid taw material as described above is supplied from the raw material supply piping 29 to an evaporator 23, and an N2 carrier gas is also supplied to the evaporator 23 from the N2 supply piping 28. A film-forming gas evaporated by the evaporator 23 is introduced through the supply piping 24 into a reaction chamber 25 together with the above-mentioned N2 carrier gas. Simultaneous with this, oxygen is introduced into the reaction chamber 25 from an oxygen tank (not shown), so that the pentaethoxy tantalum is thermally decomposed in the reaction chamber 25 to form a tantalum oxide thin film on a substrate. After the formation of the tantalum oxide thin film, the atmosphere in the reaction chanter 25 is exhausted by a discharge pump 26 through an exhaust piping 27.
In the prior art, to form a tantalum oxide thin film on a substrate uniformly, there have been proposed various configurations of the reaction chamber 25, introduction and exhaust recipes for the film-forming gas, etc.
For example, Japanese Patent Application Laid-Open No. 7-94419 discloses a semiconductor processing apparatus which is constructed as follows. A flat reaction tube is provided in a heating space defined by a pair of parallel plate heaters with a substrate to be treated being disposed in the heating space. The reaction tube is provided at it opposite ends with a gas feed port and a gas exhaust port. The direction of flow of the film-forming gas can be switched over during an film-forming operation.
FIG. 12 illustrates the reaction chamber of the semiconductor processing apparatus as described in the above-mentioned Japanese Patent Laid-Open No. 7-94419. In this figure, an unillustrated substrate is horizontally disposed substantially in the center of the interior of the reaction tube 31, and gas feed ports 32, 33 and gas exhaust ports 34, 35 are provided at opposite ends of the reaction tube 31, the gas feed ports 32, 33 being disposed in an opposed relation with respect to the gas exhaust ports 34, 35, respectively, with the substrate being interposed therebetween. For example, a gas supplied from the gas feed port 32 passes through the reaction tube 31 substantially in parallel with the substrate to be exhausted from the gas exhaust port 35, as indicated by an arrow 36 in FIG. 12, thus forming a first thin film on the substrate. Subsequently, the direction of flow of the film-forming gas is reversed, that is, the film-forming gas is supplied from the gas feed port 33 to the reaction tube 31, passing the surface of the substrate as indicated at an arrow 37, and exhausted from the gas exhaust port 34, thereby forming a second thin film on the substrate. Such a method of supplying a film-forming gas while alternately changing the direction of flow thereof is generally called a flip-flop method. The reason for adopting the flip-flop method is to counterbalance or offset an inclination that the thin film tends to have in the direction of flow of the film-forming gas, by reversing the flow of the film-forming gas.
Concretely, in cases where the film-forming gas is caused to flow in one direction from an upstream side to a downstream side along a surface of the substrate 11 so as to form a thin film thereon, as indicated at arrows 41 in FIG. 13, the thickness of the thin film thus formed tends to be thicker in a direction from the upstream to the downstream side, as illustrated in FIG. 14. The reason for this phenomenon is considered as follows. That is, generally, the internal pressure of the reaction chamber or reaction tube 31 is as low as 25 Pa or so and the flow rate or speed of the film-firming gas is high, so that the film-forming gas, being not heated until it enters the reaction chamber, has a tendency that it is activated hardly at the upstream side but easily at the downstream side. Accordingly, in the prior art, the flip-flop method is used to provide a thin film on the substrate 11 substantially in parallel to a surface thereof, as illustrated in FIG. 16, by causing the film-forming gas to flow from the upstream side to the downstream side in parallel with the surface of the substrate 11 as indicated at arrows 41 in FIG. 15, and then causing the film-forming gas to flow in a reverse direction from the downstream to the upstream side as indicated at arrows 42 to thereby offset the inclination in the thickness of the thin film. As illustrated in FIG. 16, on a first layer 51 in the form of a thin film on a substrate 11 obtained by causing a film-forming gas to flow from an upstream to a downstream side as indicated at an arrow 41, there is formed a second layer 51 in the form of a thin film by causing a film-forming gas to flow from the downstream to the upstream side as depicted at an arrow 42, and hence it is intended to provide the formation of thin films which are substantially in parallel to a surface of the substrate 11 as a whole.
However, there is a problem in that in actuality, the use of the conventional film-forming method as referred to above could not provide a good result of thin film formation as illustrated in FIG. 16.
FIG. 17 illustrates a cross section of thin films obtained by the above-mentioned Prior art technology. As is clear from this figure, the formation of thin films in parallel to a surface of a substrate 11 is not achieved although on a first layer 51xe2x80x2 in the form of a thin film that is formed by causing a film-forming gas to flow in a direction from an upstream to a downstream side as indicated at an arrow 41, there is provided a second layer 52xe2x80x2 in the form of a thin film that is obtained by causing the film-forming gas in a reverse direction from the downstream to the upstream side as indicated at an arrow 42.
The reason for this is that upon forming the thin films, the first layer 51xe2x80x2 is influenced by the surface condition of the substrate 11 which is a base or backing layer for the formation of the first layer 51xe2x80x3, so that an inclination in the thickness of the first layer 51xe2x80x2 becomes remarkable, whereas the second layer 52xe2x80x2 has a backing layer in the form of the first layer 51xe2x80x2 which is of the same material as that of the second layer 52xe2x80x3, thus providing a tendency not to create a thickness inclination. Therefore, the distribution of thickness of the thin films or layers is greatly influenced by the arrangement or condition of the first layer 51xe2x80x3, so if the inclination of the first layer 51xe2x80x2 is great, even the use of the flip-flop method could not achieve a uniform planarization of the thickness of the first and second layers.
In view of the above, an object of the present invention is to provide a semiconductor manufacturing method and a semiconductor manufacturing apparatus which are capable of achieving the formation of thin films, of a uniform thickness on a substrate.
In order to achieve the above object, according to a first aspect of the present invention, there is provided a method for manufacturing a semiconductor device including a film-forming process for causing a film-forming gas to flow over a surface of a substrate substantially in parallel therewith to form thin films on the substrate surface. The film-forming process comprises: an initial film-forming step for forming a first thin film on the surface of the substrate under a first film-forming condition; and a main film-forming step for forming, on the first thin film acting as a backing layer, a second thin film of a thickness greater than that of the first thin film under a second film-forming condition that differs from the first film-forming condition,
Pursuant to this method, the formation of the first thin film on the substrate surface in the initial film-forming step serves to suppress adverse effects which would otherwise result from the surface condition of the substrate, as a consequence of which the thin films of a uniform thickness can be formed on the substrate over the entire surface thereof according to the main film-forming step.
In this regard, note that the expression xe2x80x9cthe film-forming gas is caused to flow substantially in parallel with the surface of the substratexe2x80x9d referred to herein means that the film-forming gas is caused to flow in a predetermined direction with respect to the substrate, e.g., in a longitudinal direction thereof if the substrate takes the shape of a rectangular configuration.
In a preferred form of the first aspect of the invention, in the initial film-forming step, the film-forming gas is supplied a predetermined number of times by changing the direction of flow of the film-forming gas.
Thus, the first thin film formed in the initial film-forming step has a uniform thickness over the entire surface of the substrate, so that the second thin film of a uniform thickness can be formed on the first thin film and hence on the surface of the substrate.
Here, note that the term xe2x80x9ca predetermined number of timesxe2x80x9d referred to herein means a number of times with which there is obtained the first thin film of a substantially uniform thickness on the substrate surface capable of exhibiting an intended effect of the invention.
In another preferred form of the first aspect of the invention, the flow rate of the film-forming gas in the initial film-forming step is less than that in the main film-forming step.
Thus, the distribution of the thickness of the first thin film upon initial film forming can be made further uniform, resulting in the formation of thin films of a further uniform thickness on the substrate.
According to a second aspect of the present invention, there is provided a method for manufacturing a semiconductor device including a film-forming process for causing a film-forming gas to flow over a surface of a substrate substantially in parallel therewith to form thin films on the substrate surface, the film-forming process comprising: an initial film-forming step for forming a first thin film on the surface of the substrate; and a main film-forming step for forming, on the first thin film acting as a backing layer, a second thin film at a film-forming rate greater than that in the initial film-forming step.
Accordingly, a thin film in the form of the first thin film can be formed on the surface of the substrate in the initial film-forming step, so adverse effects which would otherwise result from the surface condition of the substrate can be suppressed, as a consequence of which a thin film in the form of the second thin film of a uniform thickness can be formed on the substrate in the main film-forming step.
According to a third aspect of the present invention, there is provided a method for manufacturing a semiconductor device including a film-forming process for forming a thin film of tantalum oxide on a surface of a substrate by using a film-forming gas including a gas evaporated from pentaethoxy tantalum, the film-forming process comprising: an initial film-forming step for forming a first thin film of tantalum oxide on the surface of the substrate under a first film-forming condition; and a main film-forming step for forming, on the first thin film acting as a backing layer, a second thin film of tantalum oxide having a thickness greater than that of the first thin film under a second film-forming condition that differs from the first film-forming condition.
Thus, using the semiconductor manufacturing method of the present invention, uniform thin films in the form of the uniform tantalum oxide films can be formed on the substrate although forming tantalum oxide films on a substrate is generally liable to be influenced by the surface condition of the substrate.
In a preferred form of the third aspect of the invention, in the film-forming process in which the film-forming gas containing a gas evaporated from pentaethoxy tantalum is used to form a tantalum oxide film on the surface of the substrate, the film-forming gas is caused to flow over the substrate surface substantially in parallel therewith.
Thus, since the first thin film formed in the initial film-forming step has a uniform thickness over the entire surface of the substrate, it is possible to provide the second thin film of a uniform thickness on the first thin film and hence on the surface of the substrate.
In another preferred form of the third aspect of the invention, the flow rate of the film-forming gas in the initial film-forming step is less than that in the main film-forming step.
Thus, since the distribution of the thickness of the first thin film upon initial film forming can be made further uniform, it is possible to form thin films of a further uniform thickness on the substrate.
According to a fourth aspect of the present invention, there is provided a method for manufacturing a semiconductor device including a film-forming process for forming a thin film of tantalum oxide on a surface of a substrate by using a film-forming gas including a gas evaporated from pentaethoxy tantalum, the film-forming process comprising: an initial film-forming step for forming a first thin film of tantalum oxide on the surface of the substrate under a first film-forming condition; and a main film-forming step for forming, on the first thin film acting as a backing layer, a second thin film of tantalum oxide having a thickness greater than that of the first thin film under a second film-forming condition that differs from the first film-forming condition; wherein the initial film-forming step and the main film-forming step are performed continuously in a common reaction chamber by means of a thermal CVD method.
Thus, using the semiconductor manufacturing method of the fourth aspect of the present invention, uniform tantalum oxide films can be formed on the substrate at low cost although forming tantalum oxide films on a substrate is generally liable to be influenced by the surface condition of the substrate.
According to a fifth aspect of the present invention, there is provided a semiconductor manufacturing apparatus comprising; a reaction chamber adapted to accommodate a substrate and having at least one gas feed port and at least one exhaust port; valves for opening and closing the at least one gas feed port and the at least one exhaust port; and a gas supply system for supplying a first film-forming gas and a second film-forming gas to the reaction chamber from the at least one gas feed port; wherein the gas supply system operates such that the first film-forming gas is caused to flow from the at least one gas feed port over a surface of the substrate substantially in parallel therewith to form a first thin film on the substrate surface under a first film-forming condition, and subsequently, the second film-forming gas is caused to flow from the at least one gas feed port over the substrate surface substantially in parallel therewith to form, on the first thin film acting as a backing layer, a second thin film of a thickness greater than that of the first; thin film under a second film-forming condition which differs from the first film-forming condition. In a preferred form of the fifth aspect of the invention, the second film-forming gas is the same as the first film-forming gas.
In another preferred form of the fifth aspect of the invention, the second film-forming gas is different from the first film-forming gas.
According to a sixth aspect of the present invention, there is provided a semiconductor manufacturing apparatus comprising: a reaction chamber adapted to accommodate a substrate and having at least one gas feed port and at least one exhaust port; valves for opening and closing the at least one gas feed port and the at least one exhaust port; and a gas supply system for supplying a film-forming gas containing a gas evaporated from pentaethoxy tantalum to the reaction chamber from the at least one gas feed port; wherein the gas supply system operates such that the film-forming gas is supplied from the at least one gas feed port to a surface of the substrate to form a first thin film of tantalum oxide on the substrate surface under a first film-forming condition, and subsequently, the film-forming gas is supplied from the at least one gas feed port to the substrate surface to thereby form, on the first thin film acting as a backing layer, a second thin film of tantalum oxide having a thickness greater than that of the first thin film under a second film-forming condition which differs from the first film-forming condition.
Thus, using the semiconductor manufacturing apparatus of the present invention, it is possible to provide uniform thin films in the form of the uniform tantalum oxide films on the substrate although forming tantalum oxide films on a substrate is generally liable to be influenced by the surface condition of the substrate.
The above and other objects, features and advantages of the present invention will become more readily apparent to those skilled in the art from the following detailed description of preferred embodiments of the invention taken in conjunction with the accompanying drawings.